1. Field of the Invention
This invention relates to the field of sound masking apparatus for producing an incoherent white or pink noise signal, and more particularly to an installation having a plurality of separate masking zones in which independent sound sources are responsive to a single remote control.
2. Prior Art
The general proposition of acoustic masking, namely the production of an incoherent audible-frequency sound for privacy or as a means to cover or mask unwanted noise has been known for some time. Recently, it has been suggested that in an open office space such as an area divided into workspaces by relatively low level partitions, a plurality of separate masking sources could be employed to provide an overall masking effect responsive to differences in the acoustic properties of the individual zones within the whole. Reference can be made, for example, to U.S. Pat. Nos. 4,438,526--Thomalla; 4,476,572--Horrall et al; 4,059,726--Watters et al; 4,054,751--Calder et al; and, 4,024,535--Goldstein. The disclosures of these patents are incorporated herein by reference.
Although the aforesaid patent to Horrall et al advocates mounting the individual units adjacent the floor in the office partitions, it is more frequently the case that the sound production elements are mounted in hollow ceilings of office spaces. One part of installation of such prior art devices is to adjust the individual units to match both the acoustic properties of the space to be masked, and also to minimize differences between adjacent zones such that masking flows smoothly from zone to zone. The patent to Thomalla teaches an active closed loop control which is operative to produce a masking signal reflecting the noise already present in the masked zone. Such a system operates by bringing the volume at a plurality of frequency ranges up to a chosen background level. Emission of noise in a given frequency range by the masking device is corresondingly reduced when a source such as a person emits a sound in that range in the controlled zone. This is an effective means to facilitate matching conditions between neighboring zones, but is expensive and complicated. Furthermore, there is no practical way of making incremental changes in the volume of the background masking noise over time, as might be required to slowly acclimate employees to a masking system, or to expand a masking system into new zones without disruption.
Volume controls are normally mounted directly on (or in) the sound generator units. In the system of Horrall et al, the sound generators are accessibly mounted. It would be possible in ceiling-mounted devices to locate a volume control means and/or an equalizer for adjusting volumes in individual frequency ranges at a position which is accessible for adjustment as needed. For example, the location could be a central control area or the area around the masking noise generator itself. Neither of these possibilities is entirely adequate. If a central control area is used for adjusting volumes, some means must be had to detect the noise present in the zone to determine the changes to be made. If the control is mounted for easy access in the area of the noise source, uniformity will be lost as changes are made in volume emissions with regard only to local effects. Furthermore, individual volume adjustments for the zones are only necessary occasionally, and including a complete volume-control device and permanent wiring for each zone is unnecessarily expensive.
According to the invention, limited access for controlling a noise source in the immediate vicinity of a mobile controller is provided by means of short range radio control. The radio controller is provided with a direct readout of the noise level detected in the zone, and may have means for inserting a signal in the background noise emitted from sources responding to the controller signal such that the user can correctly determine the noise level as a function of displacement from the noise source.
Radio remote controls are known in connection with various devices. A well-known example is the radio remote control transmitter used to control the movements of a toy vehicle such as model car or airplane. An example of such a system is shown in U.S. Pat. No. 4,080,602--Hattori et al. Different combinations of signals transmitted on a channel are decoded into vehicle movements in various directions. Typically, the controlled device is adapted such that control signals cause a momentary deflection in a controlled element such as a steering linkage. Alternatively, the presence of the signal causes operation of a motor or the like to increase or decrease the present deflection of the controlled element.
According to the invention, a volume control signal in the form of pulses is applied to ring-counter having a predetermined number of discrete intervals corresponding to volume levels. The remote control can broadcast a number of pulses equal to the capacity of the counter, resulting in no change due to a complete cycling of the ring counter. Broadcasting the full capacity count less some number of pulses will cause a decrease in volume deflection by that number of pulses. Similarly, broadcasting only a few pulses will bump the ring counter up by the corresponding amount and increase volume by that number of steps. The steps are decoded to actually select volume levels using an analog multiplexer responsive to pulse count. The use of a pulse train allows the system to take advantage of start and stop indicators, and other means of reducing problems with spurious pulses.
Selecting a volume level by adjustment of a voltage divider is known. The conventional volume control adjustment is based upon a potentiometer connected such that the wiper of the potentiometer, which selects any point of connection along an internal resistor selects the extent of voltage division. The aforesaid patent to Goldstein teaches a resistor ladder formed of a plurality of serially-connected resistors, the individual connections between resistors being accessible for connection of signals of predetermined frequency range and decibel levels. The present invention has taken a different approach to attenuation, using a plurality of remotely-controlled analog multiplexers to provide a no-moving-parts means of selecting among attentuation levels. The analog multiplexers are addressable to connect a first line to any of a plurality of second lines, as indicated by a digital address input presented on address bits. According to the invention, the binary count output bits of the attenuator's ring counter are connected to the digital address input bits of analog multiplexers, for volume step adjustments.
The device of the invention provides the optimum adjustment of individual zone masking devices. Fine volume changes are easily made to meet the individual acoustic demands of the masking zone and the personal preferences of persons therein. The ease of adjustment makes it quite easy to slowly change the masking signal volume as needed, whereby the occupants of the masked area are not distracted by a sudden increase or decrease in background masking noise. Nevertheless, according to the invention, the background masking noise can also be made to drop out during paging signals. The volume can be easily adjusted automatically or under manual remote control, for temporary or permanent changes without additional wiring or direct access to the sound source.
The device of the invention is effective as noted, is low in cost, and is extremely reliable. The invention provides full versatility and maximum convenience.